Land use is known to exert a dominant impact on a range of essential soil functions like water retention, carbon sequestration, organic matter cycling and plant growth. At the same time, land use management is known to have a strong influence on soil structure, e.g., through bioturbation, tillage and compaction. However, it is often unclear whether the differences in soil structure are the actual cause of the differences in soil functions or if they only co-occur.This impact of land use (conventional and organic farming, intensive and extensive meadow, extensive pasture) on the relationship between soil structure and short-term carbon mineralization was investigated at the Global Change Exploratory Facility, in Bad Lauchstädt, Germany. Intact topsoil cores (upper 10 cm, n=75) were sampled from all land use types at the early growing season. Soil structure and microbial activity were measured using X-ray-computed tomography and respirometry, respectively.Differences in microstructural properties between land uses were small in comparison to the variation within land uses. The most striking difference between land uses was larger macropore diameters in grassland soils due to the presence of large biopores that are periodically destroyed in croplands. Grasslands had larger amounts of particulate organic matter (POM), including root biomass, and also greater microbial activity than croplands, both in terms of basal respiration and rate of carbon mineralization during growth. Basal respiration among soil cores varied by more than 1 order of magnitude (0.08–1.42 µg CO₂-C h⁻¹ g⁻¹ soil) and was best explained by POM mass (R²=0.53, p<0.001). Predictive power was only slightly improved by considering all bulk, microstructure and microbial properties jointly. The predictive power of image-derived microstructural properties was low, because aeration did not limit carbon mineralization and was sustained by pores smaller than the image resolution limit (<30 µm). The frequently postulated dependency of basal respiration on soil moisture was not evident even though some cores were apparently water limited, as it was likely disguised by the co-limitation of POM mass. This finding was interpreted in regards to the microbial hotspots which form on decomposing plant residues and which are decoupled from water limitation in bulk soil. The rate of glucose mineralization during growth was explained well by substrate-induced respiration (R²=0.84) prior to growth, which in turn correlated with total microbial biomass, basal respiration and POM mass, and was not affected by pore metrics.These findings stress that soil structure had little relevance in predicting carbon mineralization in well-aerated soil, as mineralization appeared to by predominantly driven by the decomposition of plant residues in intact soil. Land use therefore affects carbon mineralization in well-aerated soil mainly in the amount and quality of labile carbon.

中文翻译：

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土地利用对通气良好土壤碳矿化的影响主要由颗粒有机物的变化而非土壤结构的变化来解释

众所周知，土地利用对一系列重要的土壤功能（如保水、碳封存、有机物质循环和植物生长）产生主要影响。同时，众所周知，土地利用管理对土壤结构有很大的影响，例如通过生物扰动、耕作和压实。然而，通常不清楚土壤结构的差异是土壤功能差异的真正原因还是它们只是同时发生。土地利用（传统和有机农业、集约化和粗放草甸、粗放牧场）位于德国巴德劳赫施塔特的全球变化探索设施研究了土壤结构与短期碳矿化之间的关系。完整的表土芯（上部 10 cm，n =75) 在早期生长季节从所有土地利用类型中取样。土壤结构和微生物活性分别使用 X 射线计算机断层扫描和呼吸测量法进行测量。与土地利用内部的变化相比，土地利用之间的微观结构特性差异很小。土地利用之间最显着的差异是草地土壤中较大的大孔直径，这是由于农田中存在定期破坏的大生物孔。就基础呼吸和生长过程中的碳矿化速率而言，草原具有更多的颗粒有机物（POM），包括根系生物量，并且比农田具有更大的微生物活性。土壤核心间的基础呼吸变化超过 1 个数量级（0.08–1.42  µg CO ₂-C h ^-1  g ^-1土壤），最好用 POM 质量解释（R ² =0.53，p < 0.001）。通过同时考虑所有体积、微观结构和微生物特性，预测能力仅略有提高。图像衍生的微观结构特性的预测能力很低，因为曝气不会限制碳矿化，并且由小于图像分辨率限制的孔隙维持（< 30  µ米）。尽管一些岩心明显受水限制，但经常假设的基础呼吸对土壤水分的依赖性并不明显，因为它可能被 POM 质量的共同限制所掩盖。这一发现被解释为在分解植物残留物时形成的微生物热点，这些热点与大块土壤中的水分限制脱钩。底物诱导的呼吸作用很好地解释了生长过程中葡萄糖矿化的速率（R ² =0.84) 在生长之前，这反过来又与总微生物生物量、基础呼吸和 POM 质量相关，并且不受孔隙指标的影响。这些研究结果强调，土壤结构与预测良好通气土壤中的碳矿化几乎没有相关性，因为矿化出现主要由完整土壤中植物残留物的分解驱动。因此，土地利用对通气良好土壤中碳矿化的影响主要体现在不稳定碳的数量和质量上。